The present invention relates to antennas and more particularly to antennas having stationary antenna apertures or stationary radiators that are controlled so that the direction of the antenna radiation pattern is controlled.
The radiation pattern of an antenna system whether the system be a transmitting or receiving antenna is the net pattern of all radiating apertures of the antenna (if it is a transmitting antenna) or all radiation responsive apertures of the antenna (if it is a receiving antenna). The pointing direction of the net radiation pattern of an antenna system can be changed, of course, by physically moving or rotating the system. It can also be changed without any physical movement or rotation of parts of the antenna. Two well known, common types of antenna systems wherein the direction of the net radiation pattern of the system is changed without physical movement, are referred to generally as Phased Array Antenna Systems and the Optically Scanned Antenna Systems.
Phased Array Antenna System consists of a multitude of antenna apertures (radiating elements in a transmitting antenna) disposed in a fixed array and fed via a multitude of variable phase shifters that are controlled so that the phase of power to each element is controlled. As a result of the control, the net radiation pattern of all the elements is a beacon of predetermined shape whose pointing direction from one instant to the next is changed by changing the phase of power fed to the individual radiating elements.
An Optically Scanned Antenna System usually involves a single antenna aperture for which there is a focal point. In a transmitting antenna of this sort all radiation is considered as coming from the focal point. The pointing direction of the radiation pattern of the antenna is changed by changing the location of the focal point electrically. This has been accomplished using a single radiator that has many elements coupled together that are all fed the same frequency at different amplitude and phase so that the apparent point source of net radiation from the many elements moves depending on the balance of amplitudes and phases.
In both of the above described types of antenna systems, spatial beam scanning or sweeping is accomplished by scanning amplitude and/or phase of the RF power fed to the radiating elements. For small scan angles (small scan sectors covering several beam widths), accurate scanning or pointing of the beam with negligible degradation can be achieved by using relatively few variable phase shifters. For larger scan sectors, particularly over many beamwidths, many more variable components such as phase shifters and amplitude control devices are needed. Varying phase or power continually to cause the beam to scan a sector is sometimes referred to as phase or power scanning. It is one object of the present invention to provide an antenna system without mechanically moving elements, capable of producing a radiation pattern whose pointing direction can be changed electronically using fewer variable components, and particularly, fewer variable phase shifter than used in prior systems.